[postgis-users] SRID and unprojected (Census) data

[Paragon Corporation]

For Census the SRID is 4269 and then you can reproject to 2163 (US National
Atlas - which maintains measurement at least for continental US) or a
particular UTM zone or state plane (both good for measurement but serve
smaller areas)
 or mercator (which doesn't seem terribly good for measurement but has some
other advantages such as shape and covering wider area).

To figure out the right SRID for what your native data we usually look at
the prj file if any and then run a query like this
SELECT * FROM spatial_ref_sys WHERE srtext ILIKE '%GCS%' AND srtext ILIKE
'%1983%' AND proj4text ILIKE '%NAD83%' AND proj4text ILIKE '%longlat%'

To convert to UTM zone SRID for your particular - take a look at this
function in WIKI - utmzone - it will return the SRID of UTMZone of a
geometry.

Then you can use ST_Transform to convert from 4269 to whatever you decide.

Hope that helps,
Regina and Leo

 

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Lee
Hachadoorian
Sent: Tuesday, March 11, 2008 10:35 PM
To: PostGIS Users
Subject: [postgis-users] SRID and unprojected (Census) data

Can someone please give me some ideas, or pointers to where this question is
answered elsewhere, on how to handle unprojected geographic data in PostGIS?
Would I just create the table with SRID = -1?  The US Census makes several
cartographic boundary files available using the
NAD83 datum, but unprojected (with just lat/long coordinates for each point
or polygon).  I looked through spatial_ref_sys, and there are over 500 NAD83
reference systems, but it appears that they are all projected (UTM, state
plane, whatever).

Thanks in advance,
Lee Hachadoorian
PhD Student, Geography
Program in Earth & Environmental Sciences CUNY Graduate Center
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